I've fallen completely out of practice on this dev blog, but I felt I had to mention a major milestone accomplished over the past week. The database that git-annex maintains about keys and worktree files used to only be guaranteed to be maintained for unlocked files, but it did not have information about locked files. Now it does, and it's automatically, and efficiently (I hope) kept up-to-date.
That let a long-standing bug get fixed, where when 2 files used the same key, the preferred content expression could match one file and not the other and cause get/drop to happen over and over.
But there are probably a lot of other ways this database could be used, now that's it's fully available. For example, it would be easy to write a git-annex command that queries for which worktree files use a key, without needing to scan the whole worktree to find them.